1. Field of the Invention
This invention relates to engine lubricating oils and, more particularly, to a composition for, and method of using, a custom formulated, engineered, full synthetic engine oil having a significantly longer service life, improved lubricity, lower operating cost, and fewer health, safety and environmental risks than conventional engine lubricants.
2. Description of Related Art
The use of engine lubricants in both gasoline and diesel engines is well known. Historically, virtually all engine lubricants consisted primarily of refined hydrocarbon oils into which additive packages were blended to achieve improved properties and service life as necessary to achieve certification by organizations such as the Society of Automotive Engineers (SAE). In recent years, the use of synthetic lubricating oils for gasoline engines has become more widespread. Generally speaking, the cost of synthetic oils is greater than for conventional mineral oil lubricants but synthetic oils offer improved lubricity, lower oil consumption, better engine protection and longer service life for both the lubricating oil and the engines in which it is used. With increased emphasis on the use of synthetic oils and resultant competition among suppliers, several different types of synthetic lubricants have emerged, some of which perform only marginally better than lubricants have emerged, some of which perform only marginally better than conventional oils and may not provide long term savings that justify the higher initial cost.
Full synthetic oils consist primarily of high quality synthetic polyalphaolefin (xe2x80x9cPAOxe2x80x9d) base stocks and are typically priced much higher than conventional engine lube oils. Synthetic oils are now recommended for use in some automotive engines, particularly in high performance engines and those in luxury automobiles. Generally speaking, synthetic oils are viewed as having improved lubricity and longer service life when compared to conventional motor oils. However, because PAO base stocks are significantly more expensive than refined mineral oils, many consumers have resisted switching to synthetic oils because of cost.
As a result of price sensitivity on the part of consumers, many producers of so-called xe2x80x9csyntheticxe2x80x9d oils now manufacture and market blends in which more highly refined mineral oils are used in place of most, and in some cases all, of the PAO. The percentage of synthetic base stock in blended synthetic oils (sometimes referred to as xe2x80x9cpartialxe2x80x9d synthetics) can vary, for example, from as little as about three weight percent in the lower grades up to about 30 weight percent in higher grade products, sometimes referred to as xe2x80x9cengineered blends.xe2x80x9d Such blends lack many of the improved properties previously associated with full synthetic oils containing a high percentage of PAO. Also, these lower grade xe2x80x9csyntheticxe2x80x9d lubricants may produce byproducts that foul or otherwise inhibit engine performance during use.
Beyond automotive use, the need for effective engine lubricants for diesel engines is also well known. Large diesel engines are widely used in various oilfield, industrial and transportation applications. Such engines are normally expected to remain in continuous or substantially continuous service for long periods, utilize heavier and more contaminated fuels than gasoline engines, and are frequently operated under heavy loads. In such use environments, lubricating oils that demonstrate great lubricity, long service life, lower oil consumption, better engine protection and overall cost effectiveness are often critical to the success of the related venture. Lubricity is necessary for achieving mechanical efficiency, reduced engine wear and longer intervals between major overhauls. Extended service life is desirable to reduce the out-of-service time, labor and material costs associated with oil changes. Also, by reducing the total volume of lubricating oil required to service an engine over an extended period, other cost efficiencies such as lower freight, handling and storage costs are achieved. Furthermore, longer service life, fewer oil changes and reduced transportation and handling all contribute to less worker exposure to health and safety risks, and less chance of accidental leakage or spills that can adversely affect the environment.
Lubricating oils consisting primarily of petroleum refined mineral oil and various additive packages are normally used in large diesel engines. Some synthetic oils have previously been disclosed and certified for diesel engines but their use has not become widespread. This is believed to be primarily attributable to the relatively large lubricant capacities associated with diesel engines that, when coupled with the higher selling price of synthetic lubricants, has previously been viewed as more than offsetting any related cost advantages in service life or performance. Many operators have failed, however, to fully appreciate all the costs associated with using inferior lubricants.
Diesel engines such as those used to power generators on offshore drilling platforms, for example, often have oil pans or sumps containing more than a hundred gallons of lubricating oil. Such engines are sometimes operated for 5,000 to 7,000 hours in a single year. When using a conventional lubricating oil consisting primarily of mineral oil, oil changes may be required as often as every 1,000 hours, and even more often where the diesel fuel contains more than about 0.5 weight percent sulfur or where impurities and additives in the oil contribute to the formation of sludge or acidic byproducts.
The acidity of a lubricating oil generally increases with extended use over time. As oils become more acidic, they can corrode engine parts, cause loss of power and increased repair costs. Lubricating oils typically have a total base number (xe2x80x9cTBNxe2x80x9d) in the range of about 8 to 10 when placed in service and are changed whenever the TBN drops to about 3 or 4. Where operators fail to maintain rigorous maintenance schedules and run engines with dirty or ineffective lubricant, significant engine wear can occur within relatively short periods, necessitating expensive overhauls and associated downtime.
An engineered, full synthetic lubricant is therefore needed that can be safely and effectively utilized in either gasoline or diesel-fueled engines and that will demonstrate superior performance and service life benefits which far surpass and justify any related increase in original purchase costs.
The lubricating oil disclosed herein is an engineered full PAO synthetic oil specially tailored for use as a high performance lubricant in gasoline and diesel engines. Engineered full synthetic oils are those made to the highest standards using the best PAO base stock available and are the most expensive and highest performing of the synthetic lubricating oils. These xe2x80x9cfull PAOxe2x80x9d lubricants are designed rather than refined. As used herein, the term xe2x80x9cfull PAOxe2x80x9d refers to lubricants containing only PAO as the principal base stock component, although viscosity improvers and minor amounts of other additives are used to further enhance the lubricant properties. It should be understood, however, that minor amounts of refined mineral oil may be present in the lubricants of the invention as diluents for some of the other additive components. The total amount of petroleum based oil used as a diluent in the compositions of the invention will preferably not exceed about 17 percent of the total lubricant by volume.
The synthetic engine lubricants of the invention are preferably formulated so as to meet or exceed the requirements for SAE 5W40 lubricants for gasoline or diesel engines. Such lubricants must have a product viscosity between about 12.9 and 16.7 centistokes (cs) over the requisite temperature range. The lubricants of the invention will desirably have a viscosity ranging between about 14.5 and 16.5 cs, preferably between about 15 and 16 cs, and most preferably, about 15.5 cs. Because the preferred PAO for use in the compositions of the invention has a viscosity substantially lower than that desired for the resultant lubricant, it is necessary to include components having higher viscosities in order to achieve the preferred viscosity for the overall product.
According to one preferred embodiment of the invention, a full PAO synthetic engine lubricant is provided that comprises from about 55 to about 75 volume percent, and more preferably from about 60 to about 70 volume percent, PAO having a viscosity that is preferably from about 6 to about 8 centistokes at 100xc2x0 C.; from about 5 to about 10 volume percent of a compatible ester or diester compound, preferably having a viscosity of at least about 3.5 cs, that will enhance additive solubility as well as detergency and seal swell performance of the lubricant; a viscosity index improver comprising a sufficient amount of an ethylene-propylene copolymer having a shear stability index of at least about 25, and more preferably from about 27 to 29 or greater, to produce a viscosity ranging from about 14.5 to about 16.5, and more preferably from about 15 to about 16, in the resultant lubricant; from about 12 to about 15 volume percent of a commercially available lubricant additive package such as, for example, Chevron Oronite""s OLOA 9061 to insure that the resultant lubricant meets all certification standards for an SAE 5W40 motor oil; sufficient TBN enhancer to raise the TBN of the resultant lubricant to at least 10 and preferably to at least about 12; and, if needed, a minor effective amount of a compatible antifoamant.
A particularly preferred PAO for use in the invention is a hydrogenated copolymer of 1-decene and 1-dodecene. A particularly preferred diester compound for use in the invention is diisodecyl adipate. A particularly preferred TBN enhancer for use in the invention is calcium phenate or calcium sulfonate in a diluent oil. A particularly preferred antifoamant for use in the invention is a silicone fluid such as polydimethyl(siloxane).
According to another preferred embodiment of the invention, a method for lubricating gasoline or diesel engines is disclosed that comprises the steps of providing an engine oil sump substantially devoid of leaks; filling the oil sump to an operational level with an engineered full synthetic oil as disclosed herein; while operating the engine, recirculating the oil through an external filter; periodically monitoring the total base number of the recirculating oil; and injecting into the recirculating oil a sufficient quantity of a TBN enhancer to maintain the TBN at a level of about 12.0.
According to one particularly preferred embodiment of the inventive method, the external oil filter is a centrifugal oil cleaner. According to another preferred embodiment of the invention, the TBN enhancer added to the recirculating oil comprises a high concentration of calcium phenate or calcium sulfonate in a petroleum based diluent oil, or another similarly effective, compatible TBN enhancer. According to yet another preferred embodiment of the invention, the inventive method further comprises the step of periodically monitoring the viscosity of the lubricating oil to determine whether fuel is leaking into the lubricating oil in the sump.
The engineered full PAO synthetic oil disclosed herein is most preferably installed after the engine has been run under load conditions with a mineral oil lubricant for a period sufficient to seat the piston rings. Normally this requires a minimum of 500 hours and, more preferably, about 1,000 or more hours.
The lubricant of the invention exhibits outstanding lubricity and, when used in accordance with the method of the invention, a service life more than five times longer than that experienced with conventional mineral oil lubricants, with significantly diminished health, safety and environmental risks. Furthermore, because the total volume of lubricant required is significantly lower than with mineral oil, the attendant expenses of transportation, storage and waste disposal are also reduced.